Telekiione system



J. DAVIDSON, JR

Jan. 6, 1948.

TELEPHONE SYSTEM Original Filed Dec. 50, 1958 4 Sheets-Sheet 1 INi/EI VTOR Q JDAV/DSON JR.

A TTORNEY Jan; 6, 1948. J. DAVIDSON, JR Re. 22,958

TELEPHONE SYSTEM 4 Sheets-Sheet 2 mom Original Filed Dec. '30, 1938 INVENTOR .I. vD14 V/DSON JR.

ATTORNEY Jan. 6, 1948. J. DAVIDSON; JR

TELEPHONE SYSTEM Original Filed Dec. so, 1938 4 Sheets-Sheet 3 hon Ha Ma SP 2. Q a uZOh ii INVENTOR By .104 vms o/v JR.

ATTORNEY Jan. 6, 1948. J. DAVIDSON, JR Re. 22,

TELEPHONE sYs'bEM Original Filed Dec. 30, 1938 4 Sheets-Sheet 4 IN VEN TOR J. DAVIDSON JR.

A T TORNE Y Reissued Jan. 6, 1948 UNITED STATES OFFICE 2 3.. I esteem s'rsriiii John Davidson, 1h, Montc lair; s. Jifas'sifgniir to Bell Telephone Laboratories, Incorptirated} New York, N. Y.', a corporation of liew Yorl;

01"iginall\ To.-i2,20;8,2 4 area itch. No. 248,433 December 30, 1938..

9 Serial "Ai 'iilifcaticn for. reissue November 20, 1942', Serial No.

6 that. (Cl. 159 27) This invention relates to telephone systems and particularly to special service systems such as intercepting equipments in telephone systems.

An object of the invention is to provide an improved economically arranged ringing, signaling and tripping arrangement for intercepting equipment. Heretofore, automatic telephone systems have been provided in which when a subscrib'ers line is changed or disconnected, calls therefor are extended to terminals connected to an intercepting trunk leading to intercepting apparatus for supervision by an operator. In such systems in case of an intercepting trunk circuit, for example,

extending to a distant office, the ringing is usuallytripped by the application of a ground otential on one of the conductors to operate the usual. tripping relay. In my Patent 2,209,513 of July 30, 1940, special tripping arrangements have been shown including cold cathode tubes applied toa single party subscribers line system. With this cathode tube arrangement a relay in the autornatic system isoperated to trip the ringing as soon as the connection is established to the terminals of the intercepting trunk circuit.

It is a feature of the present invention to provide circuit arrangement for intercepting calls intended for subscribers on partylines, and means is provided whereby when a party line is seized and the ringing code of the party. on said line, calls for whom are to be intercepted; is transmittedto said line, ringingis discontinued and an intercepting trunk which is associated with said line is connected for receptionoithe call. Cold cathode tubes are employed which are. responsive to particular ringing signals transmitted tothe party line representing the call for the party, calls for whom are to be intercepted.

Aspecial feature is a delay means whereby the ringing is discontinued before the trunk is prepared for the signaling of an intercepting operator to answer the call.

p The invention has been panying drawings in which:

Fig, l shows a calling subscribers line, an intermediate switch in diagrammatic form and a conector and associated terminals of an automatic tep-by -step telephone system arranged for applying ringing to a ten-party line; V l

Fig. 2 shows an intercepting trunk connected to said terminals and selectable by the connector shown in Fig. 1 for intercepting call for any particular party calls for Whom are to be intercepted, in accordance with the applicants invention;

illustrated in accom- Fig. 3 shows a connector and associated terminals of an automatic step-by-step system arranged for ringing eight or four-party lines;

Fig. 4 shows anintercepting trunk'arran'genie'nt for intercepting a call for any one of the parties on a four or eight party line, calls for whom are to be intercepted; and

Fig. 5 shows a modified portion Di an/interceptihg trunk according to Fig. 2 or 4 with the "special relay inean's omitted.

Referring nowto the drawings andparticularly to Figs; '1 and 2, terminals Hill which are 'selectaldle by a connector C shown in Fig. land normany extend to a ten-party line have also been extended to an intercepting trunk shown in Fig. 2 so that calls-for aparti'cular one of the ten parties on this line will be intercepted by an operator. The party line appears intheconnector C in the single set of terminals In'o, a1though it may, of course, be multiplied to appear similarly in other connectors; The intercepting trunk .in Fig. 2 terminates in aja'ck 200 in front of an operators position who intercepts calls directed over this trunk; i

If it is;v assumed that the last three digits of a called subscribers number which is the number of one of the arties n a tenarty line and calls fer whciii are tote intercepted, causes the brushes 'otc'oniiectcro to land the terminals I00, and the connector to transmit the desired code signals, theepera'tions' or the connector ma be as follows: The first twov ofthese three last digits locate the brushes of this connectoron the terminals mo ar d the third or last digit selects and transmits the desired code. The connecto'r may be seized by brushes IIH of a selector by connecting with the terminals or this conne'ct'or when a can comes in train a calling sutscriber such as I02 as is well known in the art. This causes the rela ms to operate over a circuit from battery and ground through the windings (if this r lay, cct tact s 6f rel y m4; terminals and the brushes of selector lot through the calling subscriberis loop. The operation of relay I03 closes-ah obvious circuit for the operation of relay I05 which is slow in releasing and remains operated during the pulses constituting succeeding digits. The operation of relay Hi5 closes a circuit for a relay. I06 from battery, lower winding of this relay, the vertical off-normal contacts I01, contacts of relay I05 to ground. The first release (of thepulsing relay I|l3 when the ll n s lh i liibfli. dials. the. first. of .these. three di its new closes, a circuit ,forthevertical magnet Hi8 from battery, winding of this magnet, conin releasing and holds over acircuit from battery through its upper winding and upper armature and front contact through the above-mentioned pulsing circuit and is consequently maintained operated during the pulsing of the digit. When this digit has been sent, the final operation of the pulsing relay I03 opens the holding circuit for relay I which now releases. On the first release of the pulsing relay I03 in response to the second digit, a circuit is closed for the rotary magnet I I0 and the relay III. The circuit for magnet IIO extends from battery through the winding of this magnet, contacts of relays II2, I06, I00, I05 and I 03 to ground and the circuit for relay I I I extends from battery through the winding of this relay over the same pulsing circuit. Relay I II is slow in releasing and is held operated by a holding circuit over its lower armature and front contact through the pulsing circuit during the pulsing of this digit. At the end of this second series of impulses, the brushes of the connector have been advanced to and connected with the terminals I00 of the desired party line.

Relay III then releases: However, if this party line is busy, relay I II remains operated long enough to permit the operation of relay I09 over a circuit from battery through the winding of this relay, contacts of relay III to ground on the sleeve terminals at I00 and when relay III is released, relay I09 is looked over make-beforebreak contacts of relay I I I to ground over its lower inner armature and front contact-and contacts of relay I05. A busy tone is thereby transmitted to the calling subscriber indicating that the line is busy. This tone circuit is extended from the busy tone source at H4, a condenser I I5, contacts of relays H2 and I09, a condenser IIB over the tip conductor to the calling subscribers telephone. If, however, the called party line is idle relay H2 is operated when relay III releases over a circuit from battery through a resistance and contacts of relay I in Fig. 2 over the sleeve terminal and brush of the connector, contacts of relay III, upper winding of rela I I2, contacts of relay I00 and I05 to ground. Relay II2 looks through a circuit from battery, its lower winding and second lower armature and front contact to ground at contacts of relay I05. Relay II2 also closes a circuit for the operation of the rotary magnet I I8 for the operation of the code selecting rotary type step-by-step switch I20. The first release of the pulse relay I03 in response to the third digit now closes a circuit for the operation of this magnet as follows: From battery through the winding of magnet II8, contacts of relays II2, I06, I09, I05 and I03. It should be noted that relay I II is also operated in this circuit as hereinbefore traced. Relay II I remains operated during the sending of the pulses of this last digit. Relay II I opens the original circuit of relay II2, but the latter relay remains operated in the locking circuit above traced. The rotary magnet IIB advances the brushes I 2| and I22 over the associated contact banks of the switch I20 to select the desired ringing code. The impulses for selecting a ringing code may, as this is a ten-party selective code ringing system, consist of from one to ten impulses. The brushes of this switch therefore will land on any one of the ten terminals as shown in the drawings and connect any one of the five generators indicated I to 5 to the corresponding terminals and brushes to leads connected to contacts of relay I25, the purpose of which will be described hereinafter. When relay II2 was operated and. while relay I I I remained operated, a circuit was completed for the operation of relay I09 from battery through the winding of this relay, contacts of relays III and H2 to ground. This ground also serves to make the line busy as it is connected to the sleeve lead. On the release of relay III, relay I09 looks over the make-beforebreak contact of relay III to a ground at relay I05. Relay III in releasing closes a circuit for relay I25 from battery, winding of this relay, contacts of relay I21, make-before-break contacts of relay I25, contacts of relays III, I09 and H2 to ground on pick-up conductor I3I as soon thereafter as the pick-up interrupter I30 reaches its next metallic segment. The connector is now ready for the transmission of the selected code to the intercepting trunk as shown in Fig. 2.

It should be noted that the trunk in Fig. 2 is provided with a key 202. This may be operated to connect a cold cathode tube 203 to the tip or the ring conductor of this intercepting trunk, depending on whether or not the called party, calls for whom are to be intercepted, is to be rung on the tip or the ring conductor by a code. If it is assumed that the key 202 is operated to connect tube 203 to the tip conductor, the call for the intercepted party is assumed to be transmitted over the tip conductor. It should also be noted that lead 204 may be connected to any one of the group of five leads 205 which are connected to five generators not shown but identified by legends generator I to generator 5 and to the first five terminals of the upper bank and to the second five terminals of the lower bank of switch I 20. The lead 204 is therefore connected to one of these five leads depending on the code of the party for whom calls are to be intercepted and if it is assumed that it is connected to the first conductor which extends to the generator No. I and the first contact on the upper bank the num ber dialed by the calling subscriber would be I'. The brushes I2I and I22 of the switch I20 would therefore be connected to the first terminals of their respective banks. On the operation of relay I25, in response to the first application of ground to pick-up conductor I3I following the release of relay III, as above described, the generator I will therefore now transmit code No. I over the first terminal of the upper bank through the brush to the lead connected to the second upper armature and front contact of relay I25, upper armature and back contact of relay I21, upper inner armature and front contact of relay II2 over the tip conductor through key 202 through the tube 203 to ground. This causes the firing of the tube 203 and a circuit is completed over the main anode of this tube from ground through the winding of relay 206, back over the tip conductor to the generator I'. This causes the operation of relay 206 which now closes a circuit through the upper armature and front contact from the generator I over the tip connection through the upper electrode 201 of the tube 208 and establishes a certain potential on this electrode. It should be noted also that the same potential from the same generator I is supplied on the lower electrode 209 of the tube 208 by the operation of relay 206 from generator I over the first conductor of the group 205, conductor 204, second lower armature and front contact of relay 206 to the electrode 209. Consenegate quently, tube 208 will not become active as these potentials are of the same value. This matching of 'the applied potentials on the two electrodes of the tube -8 identifies the code ringing for the party, calls for whom are to be intercepted, so that the trunk will be prepared for the intercepting of this call as will be further explained as the description proceeds. Some of the ringing current from generator I is diverted through the uppermost armature of pick-up relay I and the condenser to the tip conductor to supply ringing tone to the calling party. The pick-up interrupter I associated with generators :I to 5 operates to connect ground to the pick-up lead I3I, once between each transmission of the code by said generators so that when a code has been transmitted as described to the tube 208 and is completed, ground will be connected to conductor I3I from the pick-up interrupter I30 for the operation of relay 2I0. Relay 2I-0 in operating applies a ground for the operation of the delay circuit comprising the relays '2I I, 2I2 and H3. At this time, this ground applied by relay 2 I0 causes the operation of relay 2II from battery through the winding of this relay and its make-before-break contacts, contacts of relays H5, 2% and 2I-9 to ground. This ground also closes a circuit for the operation of the relay ZilI from battery through the winding of this relay and its makebefore-break contacts, contacts of relays 2I5, 206 and 2I0 to ground. Relay 20'! looks over its 'middle lower armature and front contact to the ground on the sleeve conductor applied at relay '2 and relay 2II locks over its armature and front contact, contacts of relay 2tlI to ground on the sleeve at relayII'2. Relay 225 being slow acting holds its armatures for an interval, following the opening of its locking circuit by relay 2-H), to enable relays 2H and 20I to operate and lock to the sleeve conductor. Relay 2I2 is prevented from operating at this time as long as the ground is supplied from the contacts of relay 2I0 as it is short-circuited by this ground at its upper outer armature and back contact. However, as soon as relay 2H1 releases relay 2I2 is operated over a circuit from battery winding of relay 2I2, contactsof relays 2| I, 25H, I I2 to ground over the sleeve. The tripping of the ringing code is accomplished as soon as relay 25! is operated as the tip and ring conductors are connected through the contacts of this relay to the two electrodes of the cold cathode tube 223 which therefore shunts the tip and ring conductors and causes the operation of relay I21 over a circuit extending from battery through the upper winding of relay I21, contacts of this relay, contacts of *relay I25, the first contacts on the lower bank, brush I2! and contacts of relays I25, I21, II2 over the ring conductor, contacts of relay 20I, through tube 223, contacts of relay 201 over the tip conductor, contacts of relays H2, I21, I25, brush I22, the first terminal of the upper bank to the generator I to ground. Relay I21 in operating closes a locking circuit for itself through its two windings and second lower armature and front contact to ground at relay 15. This causes the release of relay I25 which thereby disconnects the generator I from the tip conductor.

Then when the pick-up ground is again extended from pick-up interrupter I30 over lead I3I relay 2I3 operates from battery winding of relay 2I3 and its make-before-break contacts, contacts of relay 2I2, conductor I3l, pick-up interrupter I30 to ground. Relay 2I3 looks over its upper armature and front contacts through contacts of relays '2 OI and IEI Z to ground over the sleeve conductor. .R'e'lay2 t3 in operating closes a oncuit for relay M8, which circuit can be traced from ground through lower contacts of relay 2P3, over conductor 2M, and thence through relay 218 to battery, and this relay in turn closes an obvious circuit for lighting of lamp 220 to indicate to the operator that a 'c'all has been intercepted on this trunk. The purpose oi thisdelay circuit is therefore to permit the tripping of the ringing before the lamp 220 is operated and the operator has a chance to insert the plug '22I into jack 250'. When the operator answers the call by inserting plug 22I into jack 200, relay 222 operates and 'extinguishes lamp 220. Transmission battery for talking is now supplied for the calling subscriber through the winding of relay I03 and for the operator through the winding of relay I04. Relay I04 in operating reverses the battery and ground through the windings of relay 103 for supervision. Relay I-M also closes supplemental locking circuits for relays H 2 and I21. Conversation between the subscriber and operator may now begin.

If the calling subscriber disconnects first, relay I03 releases which in turn causes the release of relay I0 5. This relay removes the ground connection for the sleeve lead at its second upper armature and front contact to release the preceding switches in the usual manner and causes the release of relay I09 and when the operator disconnects relay I04 releases, causing the release of relays I21 and H2 and closes a circuit for the operation of the release magnet I40 for the connector switch and the release magnet I I-I for the ringing code selecting switch I20. The circuit for the release magnet M0 may extend from battery through the winding of this magnet, the vertical off-normal contacts I42, contacts of relays I05 and I04 to ground and the circuit for the release magnet MI for switch I20 extends from battery through the winding of this magnet, off-normal contacts I43 of the switch I20, contacts of relays I05 and I04 to ground. When these two switches are returned to normal, the circuit for the two release magnets are opened. The release of relay I-I2 disconnects the ground on the sleeve causing the release of relays 20I, 2, 212, 2I3 and 2I8. In case the operator disconnects first, the relay I04 releases and reverses the battery over the tip and ring conductors to the preceding switches and when the calling subscriber disconnects, relay I03 is released "causing the release of relays I09, I21 and I I2 and the release of the switches as described.

Assume next that a call is made for the party on the tip side of the line whose ringing code corresponds to generator 2 and that calls to this party should not be intercepted. Since as above described calls to the tip party identified by code I are to be intercepted, the code matching equipment in the intercept trunk is wired to intercept all calls corresponding to code I and to prevent the interception of calls of code 2. When, therefore, ringing current of code 2 is applied to the tip conductor of the party line, the resulting potential applied to the electrode 201 of the tube 208 fails to match throughout the ringing interval the potential applied to electrode 209 over lead 204 from the generator I. The instant the failure to match occurs the tube 238 ionizes, and current flows from a suitable source through the upper winding of relay 2I5, anode of the tube 200, cathode 201 or 209 to ground. Relay 2l5 operates and locks through its lower winding and contact to the sleeve conductor'which is grounded at the contacts of relay II2. At the end or the ringing interval ground is applied to the pick-up conductor I3l, and relay 2| operatesr In this case, however, the operation of relay 2l0 fails to operate the relays 2M and 2 because the energizing circuit is now open at the contacts of relay 2l5. The connector continues to apply ringing current of code 2 until the called party answers, and throughout this time the relay 20! remains deenergized to prevent the call from being intercepted.

Referring now to Figs. 3 and 4, which disclose an intercepting trunk connected to the terminals 300 of a fourparty or eight-party line for the interception of calls incoming to any one of the parties of these two types of lines. The connector Cl is similar to the connector 0 in Fig. 1 and operates practically in the identical manner as far as selecting a party line is concerned. The operations of this connector as far as the functions thereof in making the selection of a party line are concerned need not therefore be described in detail. It may consequently be assumed that the connector functions have progressed to the point where relay 30l has been operated. This relay corresponds to relay I25 in connector 0 and the description may therefore begin with the transmission of the third or ringing code selecting digit.

It should be noted that in Fig. 4, a key 400 may be operated to connect either the tip or the ring to the tube 402 by way of the key 403 for the reception of the code signal over the tip or the ring conductor. The key 403 has two positions and serves to connect the tip or ring, depending on the position of key 400, either to the anode or cathode of tube 402. Since the tube is unidirectional and permits current to flow only when positive potential is applied to the anode, it is thus possible to obtain four selections from the positive and negative ringing voltages applied to the tip and ring by the four combinations available with keys 400 and 403.

Ringing code selecting switch 303 is in case of a. four-party line, 01 course, only equipped for four selections by the operation of the switch 303 from one to four steps, and in the case of an eight-party line equipped as shown for eight selections. The selections of a code as determined by the setting of this switch will always cause the operation of relay 305 over a circuit from battery, Winding of this relay, contacts of relay 30l and through the brush 305 and any terminal of the associated bank to the corresponding interrupter I or 2 to interrupt the operation of this relay in accordance with the interruptions as determined by interrupter I for the first four steps or in accordance with the interruptions as determined by interrupter 2 for the last four steps to transmit superimposed ringing current over a tip or ring conductor as determined by the operation of relay 301 or 308 or both of these relays or neither of these two relays. If it is assumed that the switch 303 has been set to apply a code for the first party on any type of party line, the brush 3|0 will land on the first terminal of the associated bank and thus neither of the relays 301 or 308 will be operated. In this case superimposed negative current will be applied on the tip conductor and interrupted in accordance with the interruptions of relay 305 as determined by the interrupter I controlled by the brush 300 of the switch 303. In this case the negative superimposed current will be supplied at a source connected at BIZ, and the circuit may be traced from this source over contacts of relays 305 and 301, upper winding of relay 3! 5, contacts of relays 301, 308, 3l5 and 316, the tip conductor, key 400, key 403, in their alternate positions, the lower electrode of tube 402, the upper electrode of this tube, key 403 to ground. This causes the firing of tube 402 which thereby closes a circuit over its main anode through the upper winding of relay 404 causing this relay to operate and lock through its lower winding to ground at contacts of relay 405. When the code has been transmitted once, the usual pick-up interrupter 3|0 will supply ground on the lead 408 causing relay 405 to operate and this relay in turn applies ground through contacts of relays 404 and 408, winding of this relay to battery causing relay 408 to operate and lock over its middle lower armature and front contact over the sleeve conductor to ground at relay 3 l 5. This ground on pick-up conductor 406 also causes the operation of the first delay circuit relay 4| 0 from battery through the winding of this relay and its make-before-break contacts, contacts of relays 404 and 405 to ground. When the ground on the pick-up interrupter 3l9 is removed, the delay circuit relay 4 will operate from battery through the winding of this relay, contacts of relays M0 and 408, over the sleeve conductor to ground at relay 3|6. When relay 408 operates it connects the tip and ring conductors to the cold cathode tube 413 which then is broken down by the ringing current and closes a circuit for the operation of relay 3l5 from the negative tripping battery at 3| 8 through contacts of relay 305 when it is released, contacts of relay 301, upper winding of relay 3l5, contacts of relays 301, 308 and 3l5 over the tip conductor, contacts of relay 408 through tube 3, contacts of relay 408, back over the ring conductor, contacts of relays 3l6, 3l5 and 308 to the generator ground at 330. Relay 315 looks through its lower winding from battery, its second lower armature and front contact to the ground at relay 320. Relay 3| 5 opens the circuit for relay 30! which now releases causing the release of relay 305, causing the ringing code to be discontinued. On the next connection of ground through the pick-up interrupter 3 IS a circuit is completed for the last delay relay 4l8 from battery through the winding of this relay, make-before-break contacts of this relay, contact of relay 4ll'to the ground at the pick-up interrupter 3l9. Relay 8 closes a circuit for relay 420 which new lights lamp 42! to in'dicate to the operator that a call is waiting on this intercepting trunk. When the operator inserts her cord plug in the jack 422, relay 423 operates extinguishing lamp 42l and a circuit for relay 322 is closed over the tip and ring conductors, the talking connection is thereby established between the calling subscriber and the operator in the same manner as described in connection with Fig. 1. Relay 404 in the intercepting trunk is, of course, released as soon as the ringing code ceases. This relay, like relay 20B of Fig. 2, may be made somewhat slow to permit the operation of relays 408 and M0 following operation of relay 405.

Similarly any other code may be supplied over the tip or ring conductors by the settings of the code ringing selecting switch 303 and the consequent operations of relays 301 and 308 and various combinations. For example, it the switches select the second contact on. the, banks, relay 308 is operated from battery through. the, lower winding of this relay over the second contact through brush- 310, contacts of relay 30l to ground, This closes a circuit; for the transmission of superimposed negative ringing current over the ring. conductor from, the; source 3112, contacts of relays 305, 301, upper winding: of relay 315, contacts of relays 301, 308 and 315 over the ring conductor. To intercept calls to the corresponding party the key 400 is set in its normal position as shown, and key 403 in its alternate position. If the brushes of the code selector are advanced to the third contact, relay 301 is operated from battery, through the upper winding of this relay, third contact and brush 310 to ground at relay 30L In this case superimposed positive ringing current will be transmitted over the tip conductor from the source at 323, contacts of relays 30l, 305, 301, upper winding of 3l5, contacts of relays 301, 308, 315 and over the tip conductors. If the fourth contacts are selected, both relays 301 and 303 are operated and superimposed positive ringing current is transmitted over ring conductor. The circuit for relays 301 and 308 may be traced from battery through the lower winding of relay 301, upper winding of relay 308, the fourth contact and brush 310 to ground at contacts of relay 30l, and the circuit for the ringing current may be from the source 323, contacts of relays 301, 305, 301, upper winding of relay 315, contacts of relays 301, 308, 3l5 over the ring conductor. Similarly if the switch 303 is set to the fifth, sixth, seventh and eighth contacts, the same type of ringing current is transmitted from the sources 3l2 and 323 over the corresponding conductors as for codes I, 2, 3 and 4, but relay 305 will be interrupted at a different rate as the brush 306 will connect with the interrupter 2 in its various positions 5, 6, 1 and 8.

Since the keys 400 and 033 in the intercept trunk of Fig. 4 afford four selective conditions, it is possible to intercept calls to any one Of the parties on a four-party line. It is also possible to intercept calls on lines having more than four parties, such as partially equipped lines of the eight-party type above described provided the party whose calls are to be intercepted is the only party on the same side of the line signaled by current of the same polarity.

If Fig. 5 is inserted between the positions A and B as shown in dash-dotted lines in Fig. 2 or Fig. 4, it is evident from this figure that the delay circuit for operating the signal 220 or G2! is omitted so that when relay 20I or 408 is operated, the ringing is tripped through the tube 500 and at the same time, relay 501 is operated by the ringing current. This relay is locked to ground on the sleeve circuit. Relay 50I closes an obvious circuit for the operation of relay 218 or 420 which operates the signal 220 or 421. This arrangement may be used where it is not desired to have any delay in operating the signals.

What is claimed is:

1. In a telephone system, a calling line, a called party line, an operators position, an intercepting trunk associated with said called party line, means for establishing a connection from said calling line to said called line and for transmitting a ringing code to said party line for calling any one of the parties on said line, and means in said trunk for discontinuing the transmission of a particular" ringing, current. to said party line and for establishing aconnection over said intercepting trunk tov said operators position.

2. In a telephone system, acalling line, a called" party line, an intercepting trunk, associated with saidcalled: party: line, an operators position, means for establishing a connection from the, calling, line, to, said called line and said trunk and for transmitting different ringing codes to call corresponding parties on said party lines, means responsive to the transmission of a particular ringing code for discontinuing said transmission and for establishing a certain interval thereafter a talking connection from the calling line to said operators position over said trunk.

3. In a telephone system, a calling line, a called party line, an intercepting trunk associated with said called party line and terminat ing at said operators position, an operators position, a signal at said operators position, means for establishing a connection from the calling line to said called party line and said trunk and for transmitting different ringing codes to call corresponding parties on said party lines and means responsive to the transmission of a particular ringing code for discontinuing said transmission and for operating said signal.

4. In a telephone system, a calling line, a called party line, an intercepting trunk. an operators position, a signal, means for establishing a connection from the calling line to said called party line and said trunk and for transmitting different ringing codes to call corresponding parties on said party lines, and means responsive to the transmission of a particular ringing code for discontinuing said transmission and for operating said signal a certain time interval thereafter.

5. In a telephone system, a cal ing line, a called party line, means for establishing a connection from said calling line to said called party line in response to dial pulses, means for selecting a particular ringing code for ringing a corresponding party on said called party line in response to dial pulses and for transmitting said ringing code at intervals to said called party line, means for producing a signal during the interval between the transmission of said ringing code, an intercepting trunk connected to said called line having a normally opened talking connection, means associated with said intercepting trunk operative in response to the transmission of said particular ringing code to said called party line and to said intermediate signal for closing said talking connection and for thereafter discontinuing the transmission of the ringing code and the intermediate signal.

6. In a telephone system, a calling line, a called party line, means for establishing a connection from said calling line to said called party line in response to dial pulses, means for selecting a particular ringing code for ringing a corresponding party on said called party line in response to dial pulses and for transmitting said ringing code at intervals to said called party line, means for producing a signal during the interval between the transmission of said ringing code, an intercepting trunk connected to said called line having a normally opened talking connection, means associated with said intercepting trunk operative in response to the transmission of said particular ringing code to said called party line and to said intermediate signal for closing said talking connection and for thereafter discontinuing the transmission of ringing code and the intermediate signal, a signaling device, means operative in response to said first-mentioned signal for actuating said signaling. device a definite interval after said ringing code has been discontinued.

JOHN DAVIDSON, J R.

12 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 18,038 Schwartz Apr. '7, 1931 1,601,052 Williams Sept. 28, 1926 1,682,089 Ostline Aug. 28, 1928 

